The management of airport terminal operations has always been a daunting task due not only to the aircraft traffic in and around the airport, but also the movement of the associated ground vehicles necessary to service the aircraft. As international commerce has grown over the years, so has the amount of traffic passing through virtually every airport around the world. Industry experts are currently predicting a three-fold increase in demand for flight operations over the next twenty years. As additional flights and aircrafts are added to handle this growth, the number and size of airports, too, must grow to accommodate the increased traffic.
As it stands now, however, airports today are, in many cases, the limiting factor in aviation system capacity. Since each airport is different, each airport has a unique set of capacity limiting factors. These limiting factors include tarmac space, number of runways, number of suitable approaches, and the extent of navigational and Air Traffic Control (ATC) facilities. The continued growth of air traffic will generate additional demand for operations on the airport surface. Many airports are at or near the capacity limit for their current configuration and thus become bottlenecks for overall aviation system performance and generate significant delay.
Modern-day airport ATC procedures and general airport aviation operations procedures are based, in large part, on procedures originating from the 1950's. The ATC procedures were initially developed to ensure adequate separation between airborne aircraft, when the only surveillance system available was a radar system using a rotating radar antenna. This type of surveillance can be considered “non-cooperative” surveillance because it does not rely upon any transmissions from the aircraft to detect the presence and position of the aircraft. Specifically, the traditional radar systems calculated the position of a target using a range value based on signal transit time and the azimuth angle of the antenna. The position of the target was then usually provided on a 2-dimensional display with other detected targets, objects and clutter.
The accuracy of radar generated position data was later enhanced by early “cooperative” surveillance systems, which used transponders on the aircraft to provide aircraft identification and altitude information to ground-based receivers. These types of surveillance systems can be considered “cooperative” because the aircraft, in emitting transmission signals, is cooperating with the surveillance system. One example of such an early “cooperative” surveillance system is the Identification Friend or Foe (IFF) system, also known as the Secondary Surveillance Radar (SSR) system and Air Traffic Control Radar Beacon System (ATCRBS) system. The aircraft-supplied altitude information supplied by the IFF system removed some of the inaccuracies inherent in radar systems by providing one of the coordinate values for the target aircraft. The transponder was the key element in early cooperative surveillance systems, since without it no identification (other than visual) and no altitude information were provided to the ATC system.
These surveillance systems served the aviation system well for decades by preventing countless mishaps over the years, and are still in use today. In the 1990s, however, the FAA encouraged the development and implementation of new multi-function technologies offering superior performance compared to the radar-based systems. The first improvement came in the form of multilateration (MLAT) systems, which employed ground-based receivers around an airport to process periodic transmissions from equipped aircraft near the airport, and determined the location of the aircraft on a differential time of arrival (DTOA) basis. MLAT systems are still in use today.
Then came broadcast surveillance systems, such as automatic dependent surveillance-broadcast (ADS-B). ADS-B uses GPS technology to determine current aircraft position data on-board the aircraft itself, and then the aircraft periodically broadcasts its position and identification data. The ADS-B transmissions can be received and decoded by ground-based receivers and other ADS-B equipped aircraft to provide accurate position data to ATC operators and surrounding ADS-B equipped aircraft.
In addition to the surveillance systems described above, air traffic controllers also make use of primary surveillance radar (PSR), airport surface detection radar (ASDE) and parallel runway monitoring (PRM) radar. In order to provide all these sources of data to the air traffic controller in a manageable fashion, companies like Sensis Corporation have developed methods and systems for fusing the various data together, so that the air traffic controller sees a single output (e.g., a symbol on a 2-D display) representing a single aircraft, even though a variety of sensor data was used to determine the identity and location of that particular aircraft.
While all of these improvements have greatly increased aviation safety in and around airports, the continued growth of air traffic will present new challenges to the industry. For example, during the next two decades, global air travel demand is expected to grow by an estimated 5.2% annually and result in nearly a three-fold increase in the number of flights compared to current traffic levels. Three primary approaches will be used to accommodate this growth in demand: (a) operate more flights in non-prime hours such as nighttime; (b) expand the number of runways at busy airports; and/or (c) shift operations to other local airports that have spare capacity.
Option (a) suffers from the problem of increased noise pollution in populated areas and the associated complaints from residents. Therefore, option (a) will provide some capacity benefits but will result in more flights occurring during low visibility periods. Due to the limited amount of real estate available around existing airports, especially in metropolitan areas, it will be difficult for existing airports to exercise option (b). As airports exercise option (b) the greater sprawl of the airport's runways and taxiways will reduce the air traffic controller's ability to visually track operations for the air traffic control tower. Several airports are building taller multimillion dollar ATC towers for improved airport situational awareness to address this challenge, but as the airport becomes larger and more complex it becomes increasingly difficult to find a single location at which an air traffic control tower can provide the required visibility. Ultimately, many of these airports will have no choice but to off-load traffic to the growing number of small reliever and community airports. Small airports in turn, will seek solutions to enable growth, but will be hindered by the expenditures required for air traffic services. One of the most significant expenditures for such small airports will be the cost of a suitable ATC tower.
The current ATC procedures require the ATC operators to provide air traffic services by labor intensive hands-on control of each aircraft. While the systems described above have allowed ATC operators to be more efficient and have greatly increased safety, an integral piece of data still used by ATC operators managing airport operations is the visual data collected through their own eyes. The ability of the ATC operators to look out the window of the ATC tower and confirm, visually, what they see as a symbol generated by the surveillance systems (cooperative and non-cooperative) explains why ATC towers have a 360 degree view of the airport and its surroundings, and also explains why ATC towers are the only building of any significant height in and around the airport.
There are several problems, however, with such traditional ATC towers. The most obvious problem is the height of the tower itself. Aircraft necessarily have to maintain a significant distance from the ATC tower to avoid collision and to prevent line-of-sight interference between the ATC operators and other aircraft. Secondly, since all of the ATC operators reside within the tower, those operators have only a single perspective viewpoint of the entire airport and its surroundings. This approach is overkill for some operators who are responsible for only a certain segment of the airport (e.g., arrival and departure). A better position for those operators would be near the ends of the operative runways, but a second ATC tower at such a location would create an unacceptable obstruction for arriving and departing aircraft.
Perhaps the most significant problem with traditional ATC towers has been mentioned above—they are incredibly expensive to erect and maintain. This cost factor could prove to be the inhibiting factor for smaller “reliever” airports being able to accept an increased amount of air traffic, commensurate with what a “towered” airport could handle.
The current air traffic control model fails to leverage new and emerging technologies to increase safety while reducing costs. Thus, continued support for the current air traffic control model comprised of on-airport infrastructure and resources, including surveillance automation systems, air traffic controllers, and maintenance technicians, will require a significant and continuous investment in the air traffic infrastructure simply to meet the increasing demand while trying to maintain current safety levels. This runs counter to the aviation industry's goal of improving safety while reducing operational costs, year after year.
The operational requirements of the airport and terminal control area involve all facets of aviation, communication, navigation and surveillance. The satisfaction of these operational requirements with technological/procedural solutions needs to be based upon three underlying principles; improved safety, improved capacity and cost effectiveness. For the reasons cited above, the traditional approach of tall airport towers at every airport of moderate activity, or the requirement that every airport of moderate activity have some type of air traffic control on-site, is quickly becoming impractical.
For the reasons explained above, there is a dire need for a new ATC paradigm that does not require on-site physical ATC towers and resident operators, not to mention the maintenance infrastructure necessary to support those towers and operators.